The present invention relates to a light emitting device and a manufacturing method thereof.
As shown in FIG. 3, a light emitting device has conventionally been made up of a substrate 101, a semiconductor light emitting element 103 fixed onto the substrate 101 with use of Ag (silver) paste 102, a gold wire 104 bonded to the semiconductor light emitting element 103 and connected to an unshown electrode, two reflectors 107 disposed around the semiconductor light emitting element 103 for reflecting a light beam from the semiconductor light emitting element 103, and a resin 109 disposed between these two reflectors 107, 107 for sealing the light emitting element 103 and the gold wire 104. The reflector 107 is formed from a liquid crystal polymer having high heat resistance in consideration of influence of heat from the semiconductor light emitting element 103. A light reflecting surface 107a of the reflector 107 located on the side of the semiconductor light emitting element 103 is left untreated or mirror-finished.
However, adherence between the reflector 107 and the resin 109 is poor because the conventional light emitting device is formed such that the light reflecting surface 107a of the reflector is left untreated or mirror-finished. Consequently, there is the possibility that the reflector 107 is detached from the resin 109 due to heat generated in mounting the light emitting device or heat generated in operating the light emitting device. Proceeding in detachment of the reflector 107 from the resin 109 induces detachment of the substrate 101 from the resin 109. As a result, due to stress caused by the detachment of the substrate 101 from the resin 109, there is imposed such serious problem as destruction in connection between the semiconductor light emitting element 103 and the gold wire 104. Further, when adherence between the reflector 107 and the resin 109 is poor, water may disadvantageously invade into a detachment portion between the reflector 107 and the resin 109.
An object of the present invention is to provide a light emitting device capable of preventing detachment of a reflector from a resin.
In order to accomplish the above object, the present invention a light emitting device comprising:
a substrate;
a light emitting element on the substrate;
a reflector on the substrate for reflecting a light beam outgoing from the light emitting element; and
a resin disposed between the light emitting element and the reflector on the substrate,
wherein a face of the reflector that reflects a light beam outgoing from the light emitting element is formed into a rough surface.
According to the above configuration, the face of the reflector that reflects a light beam outgoing from the light emitting element is formed into a rough surface, so that adherence between the reflector and the resin through the rough surface of the reflector becomes relatively larger. Therefore, the reflector is hardly detached from the resin even if, for example, the light emitting device receives heat during mounting the light emitting device on the substrate or during operating the light emitting device. This ensures avoidance of such disadvantage as the substrate being detached from the resin, a bonding wire connected to the light emitting element being disconnected due to the detachment of the substrate from the resin, and water entering through a detachment portion between the reflector and the resin, thereby causing malfunction of the light emitting device.
In one embodiment of the present invention, the rough surface of the reflector has an arithmetic mean roughness ranging of 1 xcexcm or more and 20 xcexcm or less.
According to the above embodiment, adherence between the reflector and the resin through the rough surface of the reflector becomes appropriate. When the arithmetic mean roughness of the rough surface is smaller than 1 xcexcm, adherence between the reflector and the resin becomes insufficient to unavoidably cause such a problem as detachment of the reflector from the resin. When the arithmetic mean roughness of the rough surface is larger than 20 xcexcm, a reflecting amount of light on the rough reflecting surface becomes insufficient, which makes luminance of a light beam emitted by the light emitting device insufficient.
In one embodiment of the present invention, the reflector is made of a liquid crystal polymer.
According to the above embodiment, the liquid crystal polymer of which the reflector is made has good heat resistance, but has difficulty in adhering to the resin. However, since the reflector has a rough surface, sufficient adherence may be obtained between the reflector and the resin via the rough surface. Therefore, the reflector made of the liquid crystal polymer has a stable light reflecting function even if the temperature of the light emitting device is raised by light emitting operation and the like, and the problem of detachment of the reflector from the resin is avoided, which achieves stable provision of the light emitting device having good performance.
In one embodiment of the present invention, the liquid crystal polymer contains a glass at a rate of more than 0 wt % and equal to or less than 30 wt %.
According to the above embodiment, the reflector has good strength since the reflector is made of the liquid crystal polymer containing a glass. Here, when a rate of the glass contained in the liquid crystal polymer is more than 30 wt %, there increases a light beam outgoing from the light emitting element that transmits the reflector. Thereby, there is the possibility that luminance of the light emitting device may decrease and that a light beam may leak to the lateral side of the light emitting device. Also, there is a disadvantage that a mold is remarkably worn away where the reflector made of the liquid crystal polymer containing more than 30 wt % is manufactured by injection molding for example.
In one embodiment of the present invention, the liquid crystal polymer contains titanium oxide at a rate of more than 0 wt % and equal to or less than 30 wt %.
According to the above embodiment, reflectance of light increases since the reflector is made of a liquid crystal polymer containing titanium oxide. When a rate of titanium oxide contained in the liquid crystal polymer is more than 30 wt %, a resin flow of the liquid crystal polymer containing titanium oxide is deteriorated. Therefore, stable molding is not attainable when the reflector is manufactured by injection molding for example.
In one embodiment of the present invention, the liquid crystal polymer contains calcium oxide at a rate of more than 0 wt % and equal to or less than 50 wt %.
According to the above embodiment, the liquid crystal polymer containing not more than 50 wt % calcium oxide enables a rough surface to be stably formed. That is, the reflector made of the above-stated liquid crystal polymer enables formation of a rough surface having good adherence to resin. When a rate of calcium oxide contained in the liquid crystal polymer is more than 50 wt %, heat resistance and strength of the reflector decrease since a rate of the liquid crystal polymer decreases.
In one embodiment of the present invention, the liquid crystal polymer contains a glass at a rate of 20 wt % or more and 30 wt % or less, and also contains titanium oxide at a rate of 20 wt % or more and 30 wt % or less.
According to the above embodiment, the above liquid crystal polymer makes it possible to obtain a reflector having good strength and light reflectance. When the rate of the glass is less than 20 wt %, heat resistance and mechanical strength of the reflector are decreased. When the rate of the glass is more than 30 wt %, a light transmission amount of the reflector increases. Thereby, luminance of the light emitting device decreases, and a light beam leaks to the lateral side of the light emitting device. Also, When the rate of the glass is more than 30 wt %, a mold in molding the reflector is remarkably worn away. Further, when a rate of the titanium oxide is less than 20 wt %, the light reflecting rate and strength of the reflector are decreased. When the rate of the titanium oxide is more than 30 wt %, the reflector is not stably formed since a resin flow of the liquid crystal polymer containing titanium oxide is deteriorated in molding the reflector.
In one embodiment of the present invention, the liquid crystal polymer contains a glass at a rate of 5 wt % or more and 25 wt % or less, contains titanium oxide at a rate of 5 wt % or more and 25 wt % or less, and contains calcium oxide at a rate of 5 wt % or more and 25 wt % or less.
According to the above embodiment, the above liquid crystal polymer makes it possible to form a reflector having good strength and light reflectance, and a rough surface may be stably formed on the reflector, so that good adherence between the rough surface and the resin may be obtained. When a rate of the glass is less than 5 wt %, strength of the reflector becomes insufficient. When a rate of the glass is more than 25 wt %, a light transmission rate of the reflector is raised, which causes such disadvantage as shortage of luminance of the light emitting device and leakage of a light beam to the lateral side of the light emitting device. When a rate of the titanium oxide is less than 5 wt %, a light reflecting rate of the reflector is reduced. When a rate of the titanium oxide is more than 25 wt %, a resin flow is deteriorated in molding the reflector, which makes it difficult to stably form the reflector. When a rate of the calcium oxide is less than 5 wt %, it becomes difficult to stably form a rough surface on the reflector. When a rate of the calcium oxide is more than 25 wt %, heat resistance and strength of the reflector are decreased.
In one embodiment of the present invention, the resin is an epoxy resin whose glass-transition temperature is 40xc2x0 C. or more and 100xc2x0 C. or less.
According to the above embodiment, good temperature cycling resistance and reflow resistance is obtained since the resin is an epoxy resin whose glass-transition temperature is 40xc2x0 C. or more and 100xc2x0 C. or less. If the glass-transition temperature is less than 40xc2x0 C., there is the possibility that the resin is deformed in use of the light emitting device under general environments. If the glass-transition temperature is larger than 100xc2x0 C., here is the possibility that reflow resistance is deteriorated. Also, a coefficient of linear expansion of the resin is almost identical to a coefficient of linear expansion of the reflector. Therefore, detachment of the resin from the reflector is unlikely to occur even if the temperature of the light emitting device rises.
In one embodiment of the present invention, the light emitting element is wire-bonded by a gold wire, breaking strength of which is 100 mN or more at a normal temperature.
According to the above embodiment, the gold wire has breaking strength of 100 mN or more and is good in temperature cycling resistance. Therefore, the light emitting device whose light emitting element is wire-bonded by the gold wire fulfills performance stably maintained for a long period of time under the condition that rise and fall of temperature are repeated by repeated operation of the light emitting device.
The present invention also provides a method for manufacturing a light emitting device, comprising:
forming a rough-surface on a liquid crystal polymer for a reflector with use of an alkaline solution;
washing the alkaline solution;
neutralizing the alkaline solution remained on the liquid crystal polymer with use of acid; and
drying the liquid crystal polymer.
According to the above structure, the liquid crystal polymer for the reflector is exposed to the alkaline solution to form the rough surface easily and efficiently, so that the rough surface of the reflector improves adherence between the reflector and the resin.
In one embodiment of the present invention, the liquid crystal polymer for the reflector is exposed for one minute or more to the alkaline solution containing KOH at a rate of 20 wt % or more and 50 wt % or less, a temperature of the alkaline solution being 50xc2x0 C. or more so as to form the rough surface.
According to the above embodiment, the rough surface is appropriately formed on the liquid crystal polymer for the reflector.